1. Field of Invention
The present invention relates to a system (method and structural aspects) for emplacement of a conductor casing at a desired curve and orientation from an offshore platform in order to facilitate directional drilling of a well in the substratum of an offshore well site.
2. Prior Art
The reasons for directional drilling of a hydrocarbon producing well are well known. For instance, in connection with offshore production, it is the usual practice to place a stationary platform in a desired location for the optimum production of substrata hydrocarbons. From this stationary platform a number of wells are drilled.
Obviously, because of the size and location of the hydrocarbon deposits, it is necessary to penetrate the substrata at various locations according to the geological formations available for production. In order to obtain maximum production from a given platform with a number of well locations, it is necessary to drill into the substrata at various predetermined depths and orientations.
However, the initial step in the drilling process includes the installation of a surface casing which is normally, a steel pipe of relatively large diameter. In the case of offshore drilling this surface casing is commonly called the "conductor pipe". This portion of the casing system through which the well is drilled provides the "hole in the water" through which the remaining smaller casing and the drill string can be installed. The primary function of this conductor pipe is to provide the hole in the water as mentioned as well as a seal below the mudline to a predetermined depth according to the requirements of the soil conditions encountered.
Normally, the conductor pipe is installed to a depth of from 100 to 300 feet below the mudline or sea bottom. After the installation of the conductor pipe the remaining smaller casings are placed through this pipe of the desired depth and the well is drilled by means of a drill string through the series of casings.
In order to achieve a specific direction or orientation of the drill string, a number of techniques have been developed for diverting or orienting the drill string. In the usual pipe conductor, the conductor is installed in a more or less true vertical position due to the standard techniques of installation of such conductors. All directional drilling or deviated work is done below the bottom of the pipe conductor.
However, it has recently been determined that there are certain advantages to orienting the conductor pipe in a given direction by means of curving or bending the conductor below the mudline in such a manner as to orient the drilling operation towards a given target location as it leaves the end of the pipe conductor. By this means a number of advantages are gained. It is possible to reach shallower hydrocarbon formations than can be reached by diverting the drilling operation after leaving a straight vertical conductor. Greater dispersion of drilling operations can be achieved from a central single platform location. This method can also be used to avoid conflicts with previously installed conductors or operating wells on an existing platform.
In order to achieve the deviation or curvature of pipe conductors there exist three basic patents involving methods different from the novel method included herein. U.S. Pat. No. 3,670,507 (issued June 20, 1972 to Mott & Ziober, assigned to Texaco Inc.) as well as U.S. Pat. No. 3,687,204 (issued Aug. 29, 1972 to Marshall, et al, assigned to Shell Oil Co.) both depend upon the use of a series of offset staggered guides in the platform structures -- spaced so as to either accommodate a continuously precurved conductor pipe or force a conductor pipe into a curved form by means of these guides.
In addition, there exists U.S. Pat. No. 3,610,340 (issued Oct. 5, 1971 to Ziober, assigned to Texaco Inc.) which contemplates the bending or deviation of the pipe conductor by forcing it into a predrilled hole in a very hard, consolidated stratum of soil. This latter method has obvious limitations to a specific type of soil. Also, it involves the necessity for predrilling in every case.
The first two methods mentioned involving the use of a series of guides require that the platform be specifically designed for curved conductors at the design stage. That is, a platform which has been built for the normal vertical conductor installation with vertically aligned guides cannot utilize either of these methods. Thus, because of the pre-curvature of the pipe, there are limited possibilities for deviations from the predetermined curvature in the field.
For other general, prior art background information, reference is also had to U.S. Pat. No. 3,451,493 (issued June 24, 1969 to Storm) as a typical example of what is known in the art as "slant drilling" wherein the entire drilling derrick is tilted to produce directional drilling. Other general interest prior art patents are U.S. Pat. Nos. 3,610,346 (issued Oct. 5, 1971 to Ziober, assigned to Texaco Inc.) and 3,685,300 (issued Aug. 22, 1972 to Mott, assigned to Texaco Inc.), the former using pre-drilled or pre-formed guide passages in the substratum and a backward drag shoe section (element 26) at the end of the casing, while the latter uses the basic support legs of the platform which have been pre-curved as guides for directional drilling.
General reference is also had to U.S. Pat. No. 3,598,190 (issued Feb. 3, 1970 to Pfau, assigned to Shell Oil Co.) which uses deviated drilling in an offshore "Salt Dome Drilling Method" and indicates that the course of the drilling string may be deflected through a formation by use of any of the well known devices for this purpose, such as jetting, whipstocks or knuckle joints. As typical examples of directional drilling by jetting or whipstocking, the following U.S. patents are noted:
______________________________________ Pat. No. Inventors Issue Date ______________________________________ 1,900,163 D. Dana, et al 3-7-33 2,420,447 C. H. Schadel 5-13-47 2,873,092 R. P. Dwyer 2-10-59 2,953,350 S. C. Moore 9-20-60 3,000,440 R. H. Malcomb 9-19-61 3,593,810 Roger Q. Fields 7-30-71 ______________________________________
Other general interest references in the field of directional drilling in an offshore environment are noted below:
______________________________________ Pat. No. Inventors Issue Date ______________________________________ 2,565,794 G. L. Young 8-28-51 3,004,612 D. C. Kofahl 10-17-61 3,390,531 L. P. Johnston, et al 7-2-68 3,542,125 Philip S. Sizer 11-24-70 ______________________________________